Constant voltage circuit

ABSTRACT

A constant voltage circuit comprises first and second circuit terminals; a current source connected to said first and second circuit terminals; a first npn transistor whose collector is connected to the first circuit terminal through a resistor; a second npn transistor having a collector connected to the emitter of the first npn transistor, a base connected to the collector of the first npn transistor, and an emitter connected to the second circuit terminal; a third npn transistor having a base connected to the base of the first npn transistor, an emitter connected to the emitter of the first npn transistor through a resistor and a collector connected to the first circuit terminal through a resistor; a fourth transistor having a base connected to the collector of the third transistor and a collector and emitter coupled to the first and second circuit terminals; a resistor connected between the first circuit terminal and a junction of the bases of the first and third transistors; and a resistor connected between the second circuit terminal and a junction between the bases of the first and third transistors.

This invention relates to a constant voltage circuit for minimizing the voltage variation of a power supply due to a temperature variaiton.

An exposure meter using a light receiving element such as CdS etc. finds a wide application in a camera and a mercury cell is often used as a power supply for the exposure meter. The mercury cell can advantageously supply a stable voltage of about 1.3 volts, but it is liable to cause air pollution. For this reason it is desirable to use the other small type of cell. For example, a manganese cell can be used for this object. Since, however, the output voltage of the manganese cell is greatly varied, the manganese cell is proved unsatisfactory as a power supply for an exposure meter requiring a high precision.

It is accordingly the object of this invention to provide a constant voltage circuit capable of supplying a low stable output voltage.

According to one embodiment of this invention there is provided a constant voltage circuit comprising first and second circuit terminals; a first transistor of one conductivity type having a collector coupled to said first circuit terminal; a second transistor of said one conductivity type having a collector and base respectively connected to the emitter and collectors of said first transistor and an emitter connected to said second circuit terminals; a third transistor of said one conductivity type having a base and emitter respectively coupled to the base and emitter of said first transistor and a collector coupled to said first circuit terminal; a fourth transistor of said one conductivity type having a base coupled to the collector of said third transistor and a collector and emitter respectively coupled to said first and second circuit terminals; and bias means for applying a base voltage to the bases of said first and third transistors.

This invention will be further described by way of example by referring to the accompanying drawings in which:

FIG. 1 shows a constant voltage circuit according to one embodiment of this invention;

FIG. 2 shows an improved constant voltage circuit for providing a more stable output voltage with respect to a temperature variation;

FIG. 3 shows a constant voltage circuit, an improved version of the circuit in FIG. 2, for providing a small input-output voltage difference;

FIG. 4 shows a constant voltage circuit according to another embodiment of this invention in which a negative voltage is supplied;

FIGS. 5 and 6 show constant voltage circuit adapted to respectively supply output voltages two and three times the output voltage of the constant voltage circuit in FIG. 1;

FIG. 7 shows a constant voltage circuit according to another embodiment of this invention, the circuit providing a small power dissipation and a small input-output voltage difference;

FIG. 8 shows a constant voltage circuit, an improved version of the circuit in FIG. 7, for suppressing an output voltage variation; and

FIGS. 9 to 11, respectively, show modified forms of the embodiments in FIGS. 6 to 8.

FIG. 1 shows a constant voltage circuit having four pnp transistors TR₁, TR₂, TR₃ and TR₄. The transistor TR₁ has a collector connected through a resistor R₁ to an output terminal 1. A current source 2 is connected to output terminal 1 and adapted to be driven by a power supply E and supplies a current. The emitter of the transistor TR₁ is connected to the collector of the transistor TR₂, and the transistor TR₂ has a grounded emitter and a base connected to the collector of the transistor TR₁. The base of the transistor TR₁ is connected to a base of the transistor TR₃. The transistor TR₃ has an emitter connected through a resistor R₂ to the emitter of the transistor TR₁ and a collector connected through a resistor R₃ to the output terminal 1. A resistor R₄ is connected between output terminal 1 and a junction of the base of the transistors TR₁ and TR₃, and a resistor R₅ is connected between ground and the junction of the bases of the transistors TR₁ and TR₃, the resistors R₄ and R₅ providing a bias circuit for applying a bias voltage to the bases of the transistors TR₁ and TR₃. The transistor TR₄ has a base connected to the collector of the transistor TR₃, a collector connected to the output terminal 1 and an emitter connected through a resistor R₆ to ground.

The operation of the constant voltage circuit in FIG. 1 will now be explained below.

During the operation, electric current flows through the collector of the transistor TR₁ by way of the resistor R₁ and a collector voltage of the transistor TR₁ is applied to the base of the transistor TR₂. If transistors having a sufficiently large current amplification factor are used as the transistors TR₁ and TR₂, the collector voltage of the transistor TR₁ is determined by the base emitter path of the transistor TR₂. With I₁ representing a current flowing through the collector-emitter path of the transistor TR₁, and V₀ a voltage on the output terminal 1, the current I₁ will be given by

    I.sub.1 = (V.sub.0 - V.sub.BE2)/R.sub.1                    (1)

the base-emitter voltage V_(BE1) of the transistor TR₁ is automatically adjusted to a value large enough to permit a flow of the current I₁. Since the bases of the transistors TR₁ and TR₃ are connected to each other and the emitter of the transistor TR₃ is connected through the resistor R₂ to the emitter of the transistor TR₁, an emitter current I₂ flowing through the transistor TR₃ becomes smaller than the emitter current I₁ flowing through the transistor TR₁ and in consequence a voltage increasing with a rise in temperature is developed across the resistor R₂. The resistor R₃ is connected to the collector of the transistor TR₃, and a voltage having a value obtained by multiplication of a voltage across the resistor R₂ by a ratio R₃ /R₂ of the resistance of the resistor R₃ to the resistance of the resistor R₂ is generated across the resistor R₃. As a result, a voltage across the resistor R.sub. 3 is increased with a rise in temperature. On the other hand, a voltage decreasing with a rise in temperature is developed across the base-emitter path of the transistor TR₄. The values of the resistors R₂ and R₃, if properly selected, permit compensation of voltage changes caused by the temperature variation in the base-emitter voltage of the transistor TR₄ and the voltage across the resistor R₃, making it possible to maintain the voltage V₀ constant. Suppose that a voltage V₀ on the output terminal has increased for some reason or other. Then, the collector voltage of the transistor TR₃ is increased and in consequence the collector current of the transistor TR₄ is increased. Since, however, electric current from the current source 2 is virtually constant, the voltage on the output terminal is decreased. As a result, the voltage V₀ on the output terminal is maintained substantially constant.

Suppose now that in the constant voltage circuit shown in FIG. 1 transistors having a sufficiently great current amplification factor are used as transistors TR₁, TR₂ and TR₃. With I₁, I₂ and I₃ representing currents flowing through the collector-emitter paths of the transistors TR₁, TR₃ and TR₄, respectively, and V_(c3) a collector voltage of the transistor TR₃, the following equations are established: ##EQU1## where

q : electron charges

K : Bolzmann's constant (K/q = 8.66 × 10⁻⁵ V/°K)

α : constant

n : constant as determined by a transistor manufacturing method (for example, n = 1.5 for a double diffusion silicon transistor)

V_(g0) : voltage corresponding to the band gap energy of a semiconductor substrate used (for example, V_(g0) = 1.218V for silicon)

T : absolute temperature

Differentiating the equation (2) by the absolute temperature T and rearranging it yields ##EQU2## Differentiating both the terms of the equation (4) by the absolute temperature T gives ##EQU3## Substituting the equation (7) in the equation (6) and rearranging it gives ##EQU4## Differentiating the equation (3) by the absolute temperature T and rearranging it gives ##EQU5## by sybstituting the equation (8) into the equation (9), ##EQU6## By differentiating the equation (5) by the absolute temperature, ##EQU7## By substituting in the equation (11) a conditional equation ##EQU8## under which the voltage V₀ on the output terminal 1 is not varied due to a temperature variation, ##EQU9## since I₃ ≠ 0.

If, as derived from the equation (12), I₃ R₆ is a value independent of the absolute temperature, that is, if the equations (10) and (13) are equal to each other with a sufficiently great gain of the transistor TR₄, a temperature compensation in the constant voltage circuit is satisfactorily made. An output voltage V₀ substantially unaffected by the temperature variation is found from the following equation: ##EQU10## With V_(g0) = 1.218V, I₃ R₆ = 0.060V, T = 298° K, n = 1.5, V_(c3) = 0.730V, V_(BE2) = 0.720V, R₂ R₃ = 0.1 and I₂ /I₁ = 0.1, then

    V.sub.0 ≃ 1.31V

in this case, if the fourth term on the right side of the equation (14) is small enough to be negligible and

    V.sub.0 = V.sub.g0 + I.sub.3 R.sub.6 + n(KT/q)             (15)

the output voltage V₀ is obtained which is not varied due to the temperature variation. That is, when the amplification operation of transistors which are connected in the succeeding stage is taken into consideration, it will be found that, in order to effect temperature compensation of the constant voltage circuit, the constant voltage circuit should be designed so that I₃ in the equation (11) may vary in proportion to the absolute temperature. In other words, it is necessary that the following equation be satisfied. ##EQU11## Substituting the equation (16) into the equation (11) yields ##EQU12## The output voltage V₀ is found, like the equation (15), from the equation (17), ##EQU13##

If each value of the resistors R₁ and R₆ is so properly set as to fulfill the equation (15) in a case where the transistor TR₄ has a high amplification factor and the equation (18) in a case where the transistor TR₄ has a low amplification factor, a constant voltage circuit with low voltage can be obtained which is unaffected by the temperature variation. It is to be noted that the resistor R₆ can have a value of zero.

FIG. 2 is a constant voltage circuit according to another embodiment of this invention, in which the amplification degree of the transistor TR₄ is enhanced. In this Figure, like reference numerals are employed to designate elements corresponding to those shown in FIG. 1 and further explanation will be therefore omitted.

The collector of the transistor TR₄ is connected to the base of a transistor TR₈ and through a resistor R₁₀ to a constant current souce comprising pnp transistors TR₅ and TR₆, npn transistor TR₇ and resistors R₇, R₈ and R₉. The base of the transistor TR₆ is connected to the base of the transistor TR₅, the base of the latter transistor being connected to its own collector. The emitters of the transistors TR₅ and TR₆ are connected respectively through the resistors R₈ and R₉ to the positive terminal of a power supply E. The transistor TR₇ has a base connected to the base of the transistor TR₂, a collector connected to the base of the transistor TR₅ and an emitter connected to ground through the resistor R₇. The emitter of the transistor TR₈ and collector of the transistor TR₆ are connected to the base of a first stage transistor TR₉ which constitutes a Darlington circuit together with a transistor TR₁₀. The emitter of the succeeding stage transistor TR₁₀ in the Darlington circuit is connected to an output terminal, and the collectors of the transistors TR₉ and TR₁₀ are connected to the positive terminal of the power supply E.

During the operation of the constant voltage circuit a given electric current flows through the collector of the transistor TR₇ to cause a bias to be applied to the base of the transistor TR₆ and a constant current is supplied to the collectors of the transistors TR₄ and TR₈ through the emitter-collector path of the transistor TR₆. That is, a circuit including the transistors TR₄ and TR₈ is equivalently coupled to a very high load resistance and the input impedance of the Darlington circuit is very high. In consequence, a very high voltage amplification can be obtained and the variation of the output voltage V₀ is restricted to a minimum as in the case of the constant voltage circuit in FIG. 1. A capacitor C₀ is a capacitor for preventing oscillation and it is connected between the collector and the base of the transistor TR₄ so as to make the operation of the constant voltage circuit stable. A starting circuit, comprising a transistor TR₁₁ and a resistor 11, makes it easy to start the constant voltage circuit. In the absence of the starting circuit an output voltage on the output terminal 1 is not increased even when the power supply is turned ON. That is, since no electric current flows through the transistor TR₇ before the turning ON of the power supply, even when the power supply is turned ON, no electric current flows through the transistor TR₆ and in consequence the output on the voltage is maintained to be zero. The starting circuit permits electric current to flow through the resistor R₁₁ by way of the transistor TR₁₁ during the turning ON of the power supply. Since a bias voltage is applied through the resistor R₁₁ to the base of the transistor TR₆, the constant voltage circuit is immediately started. The starting circuit may be constructed of a resistor circuit and in this case the output voltage is greatly varied. If in this case the collector current of the transistor TR₇ is made great and electric current flowing through the starting circuit or the substitute resistor circuit is set to be a lowest possible value necessary to turn the transistor TR₁₁ ON, the output voltage variation can be restricted to minimum. In this embodiment, a resistor R₁₂ and diode-connected npn transistor TR₁₂ are employed in place of the resistor R₅ in the constant voltage circuit in FIG. 1. The transistor TR₁₂ has an emitter and collector connected to ground and a base connected to the resistor R₁₂. Since the base emitter voltage of the transistor TR₁₂ is decreased with a rise in temperature, a direction in which the base-biased voltage of transistors TR₁ and TR₃ is varied due to the temperature variation is the same as a direction in which the base-emitter voltage of the transistor TR₁₂ is varied due to the temperature direction. As a result, a stable operation is assured over a wide temperature variation range.

In the constant voltage circuit in FIG. 2 the output voltage is about 1.6 volts lower than the input voltage due to the presence of the transistor TR₆ and the darlington circuit comprising the transistors TR₉ and TR₁₀. In consequence, if an output voltage of, for example, 1.3V is to be obtained, an input voltage of 2.9 volts is required with the resultant poor efficiency.

A constant voltage circuit in FIG. 3 is designed to overcome such defects. In FIG. 3 an npn transistor TR₁₃ having a base connected to a junction between the collectors of transistors TR₄ and TR₆. The collector of the transistor TR₁₃ is connected to the base of a pnp transistor TR₁₄ whose emitter is connected to the power supply E. The collector of the transistor TR₁₄ is connected to an npn transistor TR₁₅ having a collector connected to its base and to the output terminal 1. The emitters of the transistors TR₁₅ and TR₁₃ are connected to each other and to a constant current source comprising an npn transistor TR₁₆ and resistor R₁₃. The transistor TR₁₆ has a collector connected to a junction between the emitters of the transistors TR₁₃ and TR₁₅, a base connected to collector of the transistor TR₁ and an emitter connected through a resistor R₁₃ to ground.

In the constant voltage circuit shown in FIG. 3 the output signal of the transistor TR₄ is amplified by the transistors TR₁₃ and TR₁₄ and it is 100% negatively fed by the transistor TR₁₅ back to the emitter of the transistor TR₁₃. In consequence, the input signal to the base of the transistor TR₁₃ and the output signal are in phase with and substantially equal in magnitude to each other. The transistors TR₁₃, TR₁₄ and TR₁₅ constitute a voltage follower circuit having a small input-output voltage difference. Since the transistor TR₁₄ is operated even in such a state that the collector-emitter voltage is lowered sufficiently to about a saturation voltage, a voltage between the positive terminal E and the output terminal 1 can be restricted to about 0.3V. If, therefore, an output voltage of, for example, 1.3V is to be obtained, an input voltage of about 1.6V may be used. When, for example, an Mn dry battery is used as a power supply, even if the power supply voltage is dropped to 1.6V, a constant voltage of 1.3V is obtained as an output voltage, providing a prominent improvement from the standpoint of economy. The same result is also obtained if a diode is used in place of the transistor TR₁₅ or if the collector of the transistor TR₁₅ is connected to the power supply E.

FIG. 4 shows a constant voltage circuit according to another embodiment of this invention, in which a power supply voltage for supplying a negative voltage may have a wide range. In this embodiment, like reference numerals are employed to designate elements corresponding to those shown in FIG. 3 and further explanation is therefore omitted.

The collector of the transistor TR₄ is connected to the collector of a transistor TR₁₇ which constitutes one element of a constant current source. The collector voltage of the transistor TR₄ is fed, through an emitter follower circuit comprising an npn transistor TR₁₈ and pnp transistor TR₁₉, to that amplification circuit, comprising a pnp transistor TR₂₀ and npn transistor TR₂₁, where it is reversed in its phase and amplified. The transistor TR₁₈ has a base connected to the collectors of the transistors TR₄ and TR₁₇, a collector connected to ground and an emitter connected to the base of the transistor TR₁₉. The emitter of the transistor TR₁₉ is connected to the base of the transistor TR₂₀ whose emitter is connected to ground. The collector of the transistor 20 is connected to the base of the transistor TR₂₁ whose collector is connected to ground.

A resistor R₁₄ and npn transistor TR₂₂ and TR₂₃ constitute a constant current source. A pnp transistor TR₂₄ and npn transistors TR₂₅ and TR₂₆ perform the same operation as the transistors TR₁₃, TR₁₄ and TR₁₅ in FIG. 3 and constitute a voltage follower circuit having a small input-output voltage difference. That is, the transistor TR₂₂ has a base connected to its own collector and an emitter connected through the resistor R₁₄ to the negative terminal of the power supply E and the transistor TR₂₃ has an emitter connected to the negative terminal of the power supply E, a base connected to the base of the transistor TR₂₂ and a collector connected to the base of the transistor TR₂₄ and to the emitter of the transistor TR₂₁. The transistor TR₂₄ has a collector connected to the base of the transistor TR₂₅ and an emitter connected to the collector of the transistor TR₂₆, and the transistor TR₂₅ has an emitter connected to the negative terminal of the power supply E and a collector connected to the emitter of the transistor TR₂₆, collector of the transistor TR₁₉ and output terminal 1. The transistor TR₂₆ has a base connected to its own collector.

An npn transistor TR₂₇ and resistor 15 constitutes a constant current source for supplying a constant electric current to the transistor TR₁₈. The transistor TR₂₇ has an emitter connected through the resistor 15 to the output terminal 1, a base connected to the base of a transistor TR₂ and a collector connected to the emitter of the transistor TR₁₈.

pnp transistors TR₂₈, TR₁₇, TR₂₉ and TR₃₀ are connected respectively to resistors R₁₆, R₁₇, R₁₈ and R₁₉, constituting constant current sources. The emitters of the transistors TR₂₈, TR₁₇, TR₂₉ and TR₃₀ are connected respectively through resistors R₁₆, R₁₇, R₁₈ and R₁₉ to ground, and the bases of the transistors TR₂₈, TR₁₇, TR₂₉ and TR₃₀ are connected to the drain of a field effect transistor TR₁₁. The transistor TR₂₈ has a collector connected to its own base and to the output terminal 1 through a resistor R₂₀, the transistor TR₂₉ has a collector connected to the emitter of the transistor TR₂₄, and the transistor TR₃₀ has a collector connected to the collector of the transistor TR₂₂.

The emitter follower circuit constituted by the npn transistor TR₁₈ and pnp transistor TR₁₉ is so incorporated into the constant voltage circuit that by increasing the input impedance of the emitter follower circuit the amplification factor of the transistor TR₄ is made great so as to restrict the output voltage variation of the constant voltage circuit to a minimum and that even if a capacitor C₀ has a small value a sufficient oscillation preventing effect is obtained. With the capacitor C₀ incorporated into the constant voltage circuit an amplification G_(V) is given, as well known in the art, by ##EQU14## where R_(s) denotes a signal source impedance R_(s) as viewed toward the signal source from the base of the transistor TR₄ and A denotes a voltage amplification factor before the capacitor is incorporated into the circuit comprising the transistor TR₄.

As will be evident from the equation (17) the capacitor C₀ is equivalent to a capacitor having (1+A) times its capacitance. As a result, a sufficiently low cut-off frequency and oscillation preventing effect are obtained. In this embodiment a sufficient oscillation preventing effect is obtained using a capacitor of, for example 20pF. The 20pF capacitor can be easily incorporated into an integrated voltage circuit.

For a -1.5V input voltage, a -1.3V output voltage unaffected by the temperature change is obtained in the constant voltage circuit shown in FIG. 4.

Although in the above-mentioned embodiment explanation is directed to the obtainment of a stable ±1.3V output voltage with a ±1.5V power supply as an input voltage, it is possible to obtain an output voltage having an integral multiple of ±1.3V.

FIG. 5 shows a constant voltage circuit as obtained by adding npn transistors TR₃₁ and TR₃₂, resistor R₂₀ and capacitor C₀ to the constant voltage circuit shown in FIG. 1. In this Figure, like reference numerals are employed to designate elements corresponding to those shown in FIG. 1 and further explanation is therefore omitted.

The transistor TR₃₁ has an emitter connected to the base of the transistor TR₄ and to ground through the resistor R₂₀ and a base connected to the collector of the transistor TR₃. The capacitor C₀ is connected to the collectors of the transistors TR₃ and TR₄ and the transistor TR₃₂ has a collector connected to the positive terminal of a power supply E, a base connected to the collector of the transistor TR₄ and an emitter connected to the output terminal 1 and to the collector of the transistor TR₃₁.

In this embodiment the emitter-base voltage of the transistors TR₄ and TR₃₁ is decreased with a rise in temperature. The decreased emitter-base voltage of the transistors TR₄ and TR₃₁ is compensated by a voltage across the resistor R₃ which is increased by the temperature increase. The constant voltage circuit provides a 2.6V stable output voltage corresponding to two times the output voltage of the constant voltage circuit in FIG. 1.

FIG. 6 shows another embodiment of this invention. This embodiment is the same as the embodiment in FIG. 5 except that an npn transistor TR₃₃ has an emitter connected to the resistor R₃ and a collector and base connected to the output terminal 1. Since the base-emitter paths of the transistors TR₄, TR₃₁ and TR₃₃ are connected in series with one another, this embodiment provides a 3.9V output voltage corresponding to three times the output voltage of the circuit in FIG. 1.

With the constant voltage circuit in FIGS. 1 to 4 as a reference voltage circuit it is possible to design a constant voltage circuit for generating a desired voltage.

FIG. 7 shows another embodiment of this invnetion. In this embodiment, like reference numerals are employed to designate elements corresponding to those shown in the above-mentioned embodiment and further explanation is therefore omitted.

In FIG. 7 the collector of the npn transistor TR₃₃ is connected to a current mirror comprising transistors TR₅, TR₆ etc. This constant voltage circuit is lower in current dissipation then the constant voltage circuit in FIG. 3 additionally including a constant current source comprising the transistor TR₇ etc. A constant current source comprising a transistor TR₃₄ and resistor R₂₁ is used in place of the resistor R₄ in the constant voltage circuit in FIG. 1. Since the constant current source can supply a necessary bias current by using a resistor sufficiently lower than the resistor R₄ in the constant voltage circuit in FIG. 3, where the constant voltage circuit is embodied as an integrated circuit, it is possible to advantageously reduce a chip size. A diode-coupled transistor TR₃₅ is cooperated with the transistors TR₃₃, TR₃₁ and TR₆ to generate an output voltage corresponding to substantially four times the voltage equivalent to the band gap energy of a semiconductor substrate used. A field effect transistor TR₃₆ for drive has a gate connected to ground, and a source and drain respectively connected to the emitter and collector of the transistor TR₃₃. Immediately after the power source is turned ON, while a voltage on the output terminal 1 is not increased, the emitter voltage of the transistor TR₃₃ is maintained to a low value, the source voltage of the field effect transistor TR₃₆ is at a low level and the bias of the transistor TR₃₆ is shallow. In consequence, a large current flows through the transistor TR₃₆ by way of the transistor TR₃₅, resistor R₁, transistor TR₂ and variable resistor R₂₂. After the constant voltage circuit is triggered, a deep bias is applied to the transistor TR₃₆ due to an increased emitter voltage of the transistor TR₃₃ and an electric current flowing through the transistor TR₃₆ is decreased, minimizing the effect exerted by the transistor TR₃₆ on the output voltage and improving the variation rate of the output voltage of the constant voltage circuit.

The resistor R₂₂ is one used to compensate for the variation of an output voltage resulting from a manufacturing error in the manufacturing processes of integrating the constant voltage circuit. The provision of one extra terminal permits the resistor R₂₂ to be adjusted from the outside. Transistors TR₃₇ and TR₃₈, respectively, serve to increase the input impedancce of transistor TR₁₃ and TR₁₅, increasing the amplification factor of the transistor TR₄. A circuit comprising a resistor R₂₃ and transistor TR₃₉ allows a relatively small current varied by a temperature variation to be applied to the transistor TR₃₁. The constant voltage circuit in FIG. 7 provides a small input-output voltage difference, a small current dissipation and a substantially constant output voltage against the temperature difference.

FIG. 8 shows a constant voltage circuit according to another embodiment of this invention. In this Figure, like reference numerals are employed to designate elements corresponding to those shown in FIG. 7 and further explanation is therefore omitted.

In FIG. 8, transistors TR₄ and TR₃₁ are driven using as a load a constant current source comprising transistors TR₄₀, TR₄₁ and TR₄₂ and resistors R₂₄, R₂₅ and R₂₆. The transistor TR₄₀ is of an npn type and has an emitter connected through the resistor R₂₄ to ground, a base connected to the corrector of the transistor TR₁ and a collector connected to the collector and base of the npn transistor TR₄₁. The transistor TR₄₁ has an emitter connected through the resistor 25 to the output terminal, and the collector connected to its own base which is connected to the base of the npn transistor TR₄₂. The transistor TR₄₂ has a collector connected to the collector of the transistor TR₄ and an emitter connected through a resistor R₂₆ to the output terminal.

The collector voltage of the transistor TR₄ is, after amplified by the transistor TR₄₃, supplied to the output terminal 1 through an emitter follower circuit comprising transistors TR₁₃, TR₁₄ and TR₁₅.

In the constant voltage circuit shown in FIG. 8 an electric current determined by the voltage of the output terminal 1 flows through the collectors of the transistors TR₄ and TR₃₁, and the transistors TR₄ and TR₃₁ provide a great amplification degree. As a result, there is provided a stable constant voltage circuit involving a small variation of an output voltage with respect to a power supply voltage and reducing the effect of the manufacturing variation of circuit elements to provide a small output variation.

FIGS. 9 to 11 show the modified forms of the embodiments shown in FIGS. 6 to 8, respectively. In the modification shown in FIGS. 9 to 11 the base of a transistor TR₃₃ is connected through a variable resistor R₂₇ to the output terminal (not connected directly to the output terminal) and through a resistor 28 to ground. An output voltage appearing on the output terminal 1 is controlled by adjusting the resistor R₂₇. In the circuit shown in FIG. 9 the base of the transistor TR₃₃ may be connected to the collector of the transistor 32, not to the output terminal 1. 

What is claimed is:
 1. A constant voltage circuit comprising first and second circuit terminals; a first transistor of one conductivity type having a collector coupled to said first circuit terminal; a second transistor of said one conductivity type having a collector and base respectively coupled to the emitter and collector of said first transistor and an emitter coupled to said second circuit terminal; a third transistor of said one conductivity type having a base and emitter respectively coupled to the base and emitter of said first transistor and a collector coupled to said first circuit terminal; a fourth transistor of said one conductivity type having a base coupled to the collector of said third transistor and a collector and emitter respectively coupled to said first and second circuit terminals; and bias means for applying a bias voltage to the bases of said first and third transistors.
 2. A constant voltage circuit according to claim 1, in which said bias means comprises a first resistive means connected between said first circuit terminal and a junction between the bases of said first and third transistors and a second resistive means connected between said second circuit terminal and a junction between the bases of said first and third transistors.
 3. A constant votlage circuit according to claim 2, further comprising a power supply terminal and a current source connected between said power supply terminal and first circuit terminal.
 4. A constant votlage circuit according to claim 2, further comprising a power supply terminal and a current source connected between said power supply terminal and second circuit terminal.
 5. A constant voltage circuit according to claim 1, further including a first resistive means connected between the first circuit terminal and the collector of said first transistor, a second resistive means connected between the emitter of said first transistor and the emitter of said third transistor, and a third resistive means connected between said first circuit terminal and the collector of said third transistor.
 6. A constant voltage circuit according to claim 5, further including a fourth resistive means connected between second circuit terminal and the emitter of said fourth transistor.
 7. A constant voltage circuit according to claim 5 in which said bias means is connected between said first circuit terminal coupled to the collectors of said first and third transistors and said second circuit terminal coupled to the emitters of said second and fourth transistors and has a power supply terminal and a current source the current source being connected between said power supply terminal and first circuit terminal.
 8. A constant voltage circuit according to claim 7, further including a capacitor connected between the collector and base of said fourth transistor.
 9. A constant voltage circuit according to claim 7, in which said current source comprises a fifth transistor of the other conductivity type having a collector connected to its own base and an emitter coupled to said power supply terminal; a sixth transistor of said other conductivity type having a base connected to the base of said fifth transistor, a collector coupled to the collector of said fourth transistor and an emitter coupled to said power supply terminal; and a seventh transistor of said one conductivity type having a collector connected to the base of said fifth transistor, an emitter coupled to said second circuit terminal and a base connected to the collector of said first transistor.
 10. A constant voltage circuit according to claim 9, in which the collector of said sixth transistor is connected through a fourth resistive means to the collector of said fourth transistor and there is further included an eighth transistor of said other conductivity type having an emitter connected to a junction between the collector of said sixth transistor and said fourth resistive means, a base connected to a junction between the collector of said fourth transistor and said fourth resistive means and a collector connected to said second circuit terminal.
 11. A constant voltage circuit according to claim 9, further including a starting means connected between the base of the sixth transistor and said second circuit terminal.
 12. A constant voltage circuit according to claim 11, in which said starting means comprises a fourth resistive means and a switching element connected in sereis with said fourth resistive means and adapted to be opened and closed in response to electric current flowing through said fourth resistive means.
 13. A constant voltage circuit according to claim 12, in which said switching element is a field effect transistor.
 14. A constant voltage circuit according to claim 11, further including an eighth transistor of said one conductivity type having a base connected to the collector of said sixth transistor and a collector connected to the power supply terminal, and a ninth transistor of said one conductivity type having a base connected to the emitter of the eighth transistor, a collector connected to the power supply terminal and an emitter connected to the first circuit terminal.
 15. A constant voltage circuit according to claim 9, further including an eighth transistor of said one conductivity type having a base connected to the collector of said sixth transistor and a collector connected to the power supply terminal, and a ninth transistor of said one conductivity type having a base connected to the emitter of the eighth transistor, a collector connected to the power supply terminal and an emitter connected to the first circuit terminal.
 16. A constant voltage circuit according to claim 15, further including a starting means which is connected between said second circuit terminal and the base of said sixth transistor and which comprises a fourth resistive means and a switching element connected in series with said fourth resistive means and adapted to be rendered on and off in response to a current flowing through said fourth resistive means.
 17. A constant voltage circuit according to claim 16, in which said switching element is a field effect transistor.
 18. A constant voltage circuit according to claim 9, further including an eighth transistor of the one conductivity type having a base connected to the collector of said sixth transistor; a ninth transistor of said other conductivity type having a base connected to the collector of said eighth transistor, and an emitter connected to said power supply terminal; a tenth transistor of said one conductivity type having a base connected to its own collector and to the collector of said third transistor through the third resistive means and an emitter connected to the emitter of said eighth transistor; and a eleventh transistor of said one conductivity type having a collector connected to a junction between the emitters of said eighth and tenth transistors, a base connected to the base of said seventh transistor and an emitter connected through a fourth resistive means to said second circuit terminal.
 19. A constant voltage circuit according to claim 18, further including a starting means connected between the base of said sixth transistor and said second circuit terminal.
 20. A constant voltage circuit according to claim 19, in which said starting means comprises a fifth resistive means and a switching element connected in series with said fifth resistive means and adapted to be opened and closed in response to electric current flowing through said fifth resistive means.
 21. A constant voltage circuit according to claim 7, in which said bias means comprises a fourth resistive means whose one end is connected to a junction between the bases of said first and third transistors, and a fifth transistor having a base connected to the other end of said fourth resistive means, and an emitter connected to said second circuit terminal.
 22. A constant voltage circuit according to claim 7, further including a fifth transistor of said one conductivity type having a base connected to a junction between said current source and the collector of said fourth transistor, a collector connected to said power supply terminal and an emitter connected through the third resistive means to the collector of said third transistor.
 23. A constant voltage circuit according to claim 22, further including a sixth transistor of said one conductivity type having an emitter connected to the base of said fourth transistor and to said second circuit terminal through a fourth resistive means, a collector connected to the emitter of said fifth transistor and a base connected to the collector of said third transistor.
 24. A constant voltage circuit according to claim 23, further including a seventh transistor of said one conductivity type having a base and collector connected to the emitter of said fifth transistor and an emitter connected through the third resistive means to the collector of said third transistor.
 25. A constant voltage circuit according to claim 23, further including a seventh transistor of said one conductivity type having an emitter connected through the first resistive means to the collector of said first transistor, a collector connected to the first circuit terminal, and a base connected to said first circuit terminal through a variable resistor and to the second circuit terminal through a resistive means.
 26. A constant voltage circuit according to claim 23, further including a seventh transistor of said one conductivity type having an emitter connected through the first resistive means to the collector of said first transistor, a collector connected to the collector of said fifth transistor, and a base connected to said first circuit terminal through a variable resistor and to said second circuit terminal through a resistive means.
 27. A constant voltage circuit according to claim 23, further including a capacitor connected between the collector of said fourth transistor and the base of said sixth transistor.
 28. A constant voltage circuit according to claim 7, in which said current source comprises a fifth transistor of the other conductivity type having an emitter connected through a fourth resistive means to said power supply terminal and a collector connected to its own base; a sixth transistor of said other conductivity type having a base connected to the base of said fifth transistor, a collector connected to the collector of said fourth transistor and an emitter connected through a fifth resistive means to said power supply terminal; a seventh transistor of said one conductivity type having a collector connected to the collector of said fifth transistor; and an eighth transistor of said one conductivity type having a base connected to its own collector and to the collector of said seventh transistor and an emitter connected through the first resistive means to the collector of said first transistor and in which there are further included a field effect transistor having a drain and source respectively connected to the collector and emitter of said seventh transistor and a gate connected to said second circuit terminal; a ninth transistor of said one conductivity type having a base connected to the collector of said sixth transistor; a tenth transistor of said other conductivity type having a base connected to the collector of said ninth transistor and an emitter connected to said power supply terminal; an eleventh transistor of said one conductivity type having a base connected to its own collector and base of said seventh transistor and an emitter connected to the emitter of said ninth transistor; and a twelfth transistor of said one conductivity type having a base connected to the base of said second transistor, a collector connected to a junction between the emitters of said ninth and eleventh transistors, and an emitter connected through a sixth resistive means to said second circuit terminal.
 29. A constant voltage circuit according to claim 28, further including a variable resistor connected between said first circuit terminal and the base of said seventh transistor, and a resistive means connected between said second circuit terminal and the base of said seventh transistor.
 30. A constant voltage circuit according to claim 28, in which the collector of said sixth transistor is connected through a seventh resistive means to the collector of said fourth transistor and which further includes thirteenth transistor of said other conductivity type having an emitter connected to a junction between said seventh resistive means and the collector of said sixth transistor, a base connected to a junction between said seventh resistive means and the collector of said fourth transistor, and a collector connected to the second circuit terminal.
 31. A constant voltage circuit according to claim 28, further including a thirteenth transistor of said one conductivity type having an emitter connected to the base of said fourth transistor and to said second circuit terminal through a seventh resistive means, a collector connected to the collector of said fourth transistor and a base connected to the collector of said third transistor.
 32. A constant voltage circuit according to claim 31, in which said seventh resistive means includes a fourteenth transistor of said one conductivity type having a base and collector connected through a resistive means to the emitter of said thirteenth transistor and an emitter connected to said second circuit terminal.
 33. A constant voltage circuit according to claim 28, further including a thirteenth transistor of said one conductivity type having a collector connected to the collector of said sixth transistor and a base connected to the base of said eleventh transistor; a fourteenth transistor of said other conductivity type having an emitter connected through a seventh resistive means to the base of said thirteenth transistor and a collector connected to the collector of said fourth transistor; a fifteenth transistor of said other conductivity type having an emitter connected through a eighth resistive means to the base of said thirteenth transistor and a base connected to its own collector and base of said fourteenth transistor; and a sixteenth transistor of said one conductivity type having a collector connected to the collector of said fifteenth transistor, a base connected to the base of said twelfth transistor and an emitter connected through a resistive means to said second circuit terminal; and a seventeenth transistor of said other conductivity type having an emitter connected to the emitter of said thirteenth transistor, a collector connected to said second circuit terminal and a base connected to the collector of said fourth transistor.
 34. A constant voltage circuit according to claim 7 in which said current source comprises fifth to eighth transistors of the other conductivity type the emitters of which are connected respectively through fourth to seventh resistive means to said first circuit terminal and the bases of which are connected in common with each other, the collector and base of said fifth transistor being connected to each other, the collector of said fifth transistor being connected to said second circuit terminal and the collector of said sixth transistor being connected to the collector of said fourth transistor, and in which there are further included a ninth transistor of said one conductivity type having a collector connected to said first circuit terminal and a base connected to the collector of said third transistor; a tenth transistor of said one conductivity type having a collector connected to the emitter of said ninth transistor, a base connected to the collector of said first transistor and an emitter coupled to the emitter of said second transistor; an eleventh transistor of said other conductivity type having a base connected to the emitter of said ninth transistor and a collector connected to the emitter of said second transistor; a twelfth transistor of said other conductivity type having a base connected to the emitter of the eleventh transistor and an emitter connected to said first circuit terminal; a thirteenth transistor of said one conductivity type having a base connected to the collector of said twelfth transistor and a collector connected to said first circuit terminal; a fourteenth transistor of said one conductivity type having a collector connected to the emitter of said thirteenth transistor and an emitter connected to said power supply terminal; a fifteenth transistor of said one conductivity type having a collector connected to its own base and collector of said eighth transistor and an emitter coupled to said power supply terminal; a sixteenth transistor of said other conductivity type having a base connected to the collector of said fourteenth transistor; a seventeenth transistor of said one conductivity type having a collector connected to its own base, emitter of said sixteenth transistor and collector of said seventh transistor; an eighteenth transistor of said one conductivity type having a collector connected to the emitter of said seventeenth transistor, a base connected to the collector of said fifteenth transistor and an emitter connected to said power supply terminal; and an eighth resistive means and switching element connected between said power supply terminal and the bases of said fifth to eighth transistors, said switching element being adapted to be opened and closed in response to electric current flowing through said eighth resistive means.
 35. A constant voltage circuit according to claim 1, further comprising a power supply terminal and a current source, the current source being connected between said power supply terminal and first circuit terminal.
 36. A constant voltage circuit according to claim 1, further comprising a power supply terminal and a current source, the current source being connected between said power supply terminal and second circuit terminal.
 37. A constant voltage circuit according to claim 1, further including a first resistive means connected between said second circuit terminal and the emitter of said fourth transistor. 